Field of the Invention
The present invention relates to a microphone device favorably used in conference rooms and the like, and especially relates to a microphone device including light emitting elements, which can suppress occurrence of noises based on switching of lighting and non-lighting of the light emitting elements included in the microphone.
Description of the Related Art
For example, as conference microphones installed on speech tables of conference rooms or tables of conference attendees, gooseneck-type microphones are provided. The gooseneck-type microphones include a stand arm with a long neck and including a flexible pipe that easily enables angle or height adjustment, and a microphone case in which a microphone unit is housed is attached to a tip portion of the stand arm.
As the gooseneck-type microphones, typically, a small and light condenser microphone is used, and a phantom power feed system is employed in order to operate an impedance converter of the condenser microphone, the phantom power feed system being able to obtain an operation power supply from a microphone amplifier unit side, such as a mixer, using a signal line of the microphone.
In the above-described microphones installed in conference rooms or the like, a microphone including a light emitting element therein is provided in order to have smooth progress of conferences, and a light bulb or an LED is used as the light emitting element.
Currently, in many of these types of microphones, LED which consumes little power and has good visibility is used as the light emitting element.
FIG. 1 illustrates an example of a gooseneck-type microphone including light emitting elements. A gooseneck-type microphone 1 illustrated in FIG. 1 is configured from a base portion 2 detachably mounted to a socket attached on a conference desk or a desk surface, a stand arm 3 attached to the base portion 2, and a microphone case 4 attached to an upper end portion of the stand arm 3.
The stand arm 3 is configured from a center relay pipe 3a, and flexible pipes 3b and 3c attached to upper and lower both ends of the relay pipe 3a. 
Further, a condenser microphone unit and an audio signal output circuit including an impedance conversion circuit described below are housed in the microphone case 4 attached to the upper end portion of the stand arm 3. Further, a plurality of light transmission holes 4a is formed along a peripheral side surface of the microphone case 4, and the light transmission hole 4a is embedded with a translucent resin material. Light from LEDs (not illustrated) as the light emitting elements housed in the microphone case 4 is projected to an outside through the translucent resin material of the light transmission holes 4a. 
The LEDs as the light emitting elements mounted on the gooseneck-type microphone 1 is subjected to lighting (light emission) and non-lighting operations by remote control by a chairman of a conference or an operator who can overlook the entire conference room. Accordingly, the chairman can prompt a speaker with a lighted light emitting element to speak, and can smoothly advance the conference.
By the way, as a power supply that lights the LEDs as the light emitting elements mounted on each microphone, two means can be considered, which include means to supply a power supply independent of an outside, and means to use a power supply to be supplied to the audio output circuit of the microphone.
When the latter means to use a power supply to be supplied to the microphone is used, there are advantages that only a control signal line that controls lighting and non-lighting of the light emitting elements may just be wired, and it is not necessary to separately supply a current that lights the LEDs as the light emitting elements.
FIG. 2 illustrates a circuit example of a conventional microphone device 1 that lights an LED using a power supply to be supplied to an audio output circuit of a microphone.
The reference sign 5 in FIG. 2 illustrates a condenser microphone unit. An output of the condenser microphone unit 5 is subjected to impedance conversion, and is output from an output terminal (output connector) 8 as a balanced output signal by an audio signal output circuit 6.
This output terminal 8 is a three-pin type connector including a first pin P1 for grounding, a second pin P2 used as a hot side of a signal, and a third pin P3 used as a cold side of the signal. A signal from the microphone 1 is sent to a microphone amplifier unit such as a mixer (not illustrated) through a microphone cable (balanced shield cable (not illustrated)) connected to the output terminal 8.
Further, a direct current equally divided through the second pin P2 and the third pin P3 of the output terminal 8 is sent from a phantom power feed circuit included in the microphone amplifier unit side such as the mixer to the microphone 1 side. Then, a light emitting drive current is supplied to the above-described audio signal output circuit 6 including the impedance conversion circuit, and a display circuit 9 including an LED (D1) as the light emitting element, using a direct current drive voltage generated in a power supply circuit 7 arranged at the microphone 1 side.
Note that configurations of the audio signal output circuit 6 including the impedance conversion circuit and the power supply circuit 7 illustrated in FIG. 2 are the same as an embodiment according to the present invention illustrated in FIG. 3 described below. Therefore, in FIGS. 2 and 3, a portion serving the same function is denoted with the same reference sign, and details thereof will be described below based on FIG. 3.
In the configuration illustrated in FIG. 2, the display circuit 9 that performs lighting and non-lighting of the LED (D1) as the light emitting element mounted on the microphone 1 by remote control, using the direct current power supply by the power supply circuit 7, is included.
That is, an anode of the LED (D1) is connected to the display circuit 9 through a resistance R7 that receives a drive current from the power supply circuit 7 and a constant current diode CR2, and a cathode of the LED (D1) is connected to a ground. Then, a condenser C7 is inserted between a connection point of the resistance R7 and the constant current diode CR2, and the ground, and an N-type MOS-field effect transistor (Q5) is connected in parallel to the LED (D1). Then, a gate of the MOS-field effect transistor (Q5) is connected to a signal line connector 10.
A remote control operation unit 11 that performs a blinking operation of the LED (D1) is connected to the signal line connector 10 at the microphone device 1 side through a connector 12. A resistance R9 and a manual switch S1 are connected in series and arranged between a direct current operation power supply Vcc and the ground in the remote control operation unit 11. Then, a connection point of the resistance R9 and the manual switch S1 is connected to a Schmitt trigger circuit ST that functions as a waveform forming circuit. An output of the Schmitt trigger circuit ST is supplied to an inverter circuit IN, and an output of the inverter circuit IN is supplied to a gate of the MOS-field effect transistor (Q5) at the microphone device 1 side through the connectors 12 and 10.
According to the circuit configuration illustrated in FIG. 2, the manual switch S1 included in the remote control operation unit 11 is operated to ON, so that a voltage level supplied to the Schmitt trigger circuit ST is made to the ground (L level). Accordingly, an output potential of the Schmitt trigger circuit ST becomes an “H” level that is close to the direct current operation power supply Vcc.
The output of the Schmitt trigger circuit ST is inverted by the inverter circuit IN. Therefore, a potential supplied to the gate of the MOS-field effect transistor (Q5) at the microphone device 1 side is made to the “L” level, and the MOS-field effect transistor (Q5) becomes an OFF state.
Therefore, the current from the power supply circuit 7 included in the microphone 1 is supplied to the LED (D1) connected in parallel to the MOS-field effect transistor (Q5), and the LED (D1) is lighted.
Note that, when the manual switch S1 included in the remote control operation unit 11 is operated to OFF, functions of the above-described “H” level and “L” level are inverted, and the MOS-field effect transistor (Q5) is made to an ON state. As a result, the current flowing in the LED (D1) is decreased, and the LED (D1) is made to a lights-out state.
The microphone device which includes the power supply circuit 7 that provides the drive current to the audio signal output circuit 6 including the impedance conversion circuit of the condenser microphone, and which lights the LED as the light emitting element using the current from the power supply circuit 7, as illustrated in FIG. 2, is disclosed in Japanese Patent No. 4528465 (hereinafter, called Patent Document 1).
By the way, the microphone device disclosed in Patent Document 1 is configured to provide the drive current from the power supply circuit 7 to the audio signal output circuit 6 including the impedance conversion circuit and the display circuit 9 including the LED. That is, the audio signal output circuit 6 and the display circuit 9 are connected in parallel to the power supply circuit 7. Therefore, when an operation to blink the LED (D1) is performed, a power supply voltage of the power supply circuit 7 fluctuates, and a drain voltage of the field effect transistor (Q1) that configures the impedance conversion circuit and an operation voltage of the audio signal output circuit 6, for example, also fluctuate in association with the fluctuation of the power supply voltage of the power supply circuit 7, and a problem that the fluctuation of the operation voltage of the audio signal output circuit is immediately superimposed on an audio signal as noises occurs.
To suppress the occurrence of the noises, in the circuit configuration illustrated in FIG. 2, the resistance R7 and the condenser C7 are arranged in the display circuit 9, and means to make the fluctuation of the power supply voltage associated with blinking of the LED (D1) moderate is applied. In this case, by setting a value of the resistance R7 to be large, the occurrence of the noises can be further suppressed. However, a voltage value applied to the LED is decreased, and thus it becomes difficult to light a plurality of LEDs at the same time to enhance visibility of the LEDs.